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P. 699. The Gas Engine.—Beau de Rochas shewed the
necessity for large cylinder volume and small circumference, high
piston speed, large expansion, and high initial pressure, proposing
also his four-stroke cycle, where he used compression to give
opportunity for sustained expansion. The defects of this cycle
are irregular crank effort, dilution of charge with burnt gases, and
expansion-ratio no larger than compression-ratio.
Other Cycles.—In Clerk's engine of 1880, Fig. 874, the charge
is first prepared in the displacer cylinder whose strokes are :
s»—>• admission of charge, first gas and air, afterwards air,
4-m slight compression, and expulsion to motor.
The motor crank follows that of displacer by 90°, and the
motor-cylinder operations are